Referring to FIGS. 1A and 1B, a conventional lamp contains a housing 11′, plural lighting tubes 12′, and an electrical connecting member 13′, wherein each lighting tube 12′ is in a U shape and has a filament fixed therein, mercury fed therein, and fluorescent substances coated thereon, thus illumining lights after connecting with an external power supply. Referring to FIG. 1B, another lamp 1′ has a spiral lighting tube 12′ formed thereon. However, such two conventional lamps cause electromagnetic waves to hurt user's body, and the mercury and UVs harms the user body as well. Likewise, color rendering index of the two conventional lamps are limited within 80 to 90, and the two conventional lamps are manufactured at high cost.
As shown in FIGS. 2A and 2B, a conventional LED lamp 2′ contains: a holder 21′, an insulation seat 22′, four circuit boards 23′, plural LED elements 24′, and a cover 25′. The four circuit boards 23′ are accommodated on an accommodating portion 211′ of the holder 21′ by means of the insulation seat 22′. The plural LED elements 24′ are fixed on the four circuit boards 23′ and are controlled by a circuit driving module 26′ to illumine lights.
However, the conventional LED lamp 2′ has following defects:
1. The lamp 2′ does not contain any LED elements 24′ arranged on a top end thereof, so it cannot illumine the lights omnidirectionally.
2. After illuminating the lights from the plural LED elements 24′, heat from the plural LED elements 24′ cannot be dissipated efficiently. In other words, the heat gathers on the four circuit boards 23′ to damage the plural. LED elements 24′ or the circuit driving module 26′ easily. In addition, the holder 21′ of FIG. 2B has a plurality of heat dissipation fins 212 formed around a peripheral side thereof, but the circuit board 23′ is made of fiberglass material, thus conducting the heat difficulty.
3. Since the conventional LED lamp 2′ cannot dissipate the heat effectively, it cannot be applied at high power (>20 W).
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.